Method for managing a hybrid compressor of an air-conditioning circuit

ABSTRACT

The invention relates to a method for managing a hybrid compressor ( 10 ) for an air-conditioning circuit of a motor vehicle having a heat engine, said hybrid compressor being suitable for being driven, on the one hand, by said heat engine and, on the other hand, by an electric motor ( 20 ) during phases in which the drive of the compressor ( 10 ) by means of the heat engine is interrupted. According to the invention, during a phase in which the drive is interrupted, said method comprises starting said electric motor ( 20 ) before said drive interruption begins. The invention can be used for air-conditioning motor vehicles having a heat engine and provided with an automatic stopping and restarting system.

The present invention relates to a method for managing a hybridcompressor for an air-conditioning circuit of an engined motor vehicle.

The invention finds a particularly advantageous application in the fieldof the air-conditioning of engined motor vehicles equipped with anautomatic stopping and restarting system, such as the systems able toimplement the function known by the term “Stop and Start”.

The “Stop and Start” function consists, under certain conditions, inautomatically causing the complete stopping of the engine when thevehicle itself has stopped, and then in automatically restarting theengine following, for example, an action of the driver interpreted as arestart request.

A typical situation for implementing the “Stop and Start” function isthat of stopping at a red light. When the vehicle stops at the light,the “Stop” mode of the “Stop and Start” function causes the automaticstopping of the engine, and the vehicle then enters the “Start” modewhich allows the engine to restart automatically without it beingnecessary to use the means for initial starting of the motor, such as acontact key for example. When the light turns green, the “Start” modeautomatically restarts the motor, especially by means of analternator-starter, following the detection by the command system uponthe starting of the vehicle of the depression by the driver of theclutch pedal, of the accelerator pedal, or else of any other action thatcan be interpreted as the driver's desire to restart his vehicle. Thebenefit of the “Stop and Start” function is understood in terms ofenergy saving and pollution reduction, particularly in urbansurroundings.

Moreover, it is known that an air-conditioning circuit of an enginedvehicle comprises a refrigerant fluid compressor which is driven by theshaft of the crankshaft of the engine by way of a belt and a pulleylinked mechanically to the rod of the compressor. Stated otherwise, theair-conditioning circuit of the vehicle can only operate if the engineis driving the compressor. Consequently, during the vehicle stoppingphases in the context of the “Stop and Start” function, the compressoris no longer driven by the engine and the air-conditioning ceases tooperate. It follows from this that in the course of these stoppingphases the setpoint temperature inside the cabin may not be maintained,and this can cause a feeling of discomfort for the passengers of thevehicle.

To ensure the maintaining of the temperature in the cabin during thephases of stopping of driving of the compressor by the engine, it isproposed to replace, for example, the usual compressor driven by theengine of the vehicle by a hybrid compressor consisting of two separatecompression chambers, constituting, on the one hand, a so-calledmechanical compressor whose rod is driven by the engine in the samemanner as the usual compressor and, on the other hand, a so-calledelectric compressor whose rod is driven by an auxiliary electric motor.The rods of two compression chambers are independent.

When the engine is running, outside of the stopping phases determined bythe “Stop and Start” function, the refrigerant fluid circulates in theair-conditioning circuit through the mechanical compressor driven by theshaft of the crankshaft of the engine, while the electric compressor isturned off. Conversely, during the phases of stopping of the “Stop andStart” function, the refrigerant fluid is directed toward the electriccompressor, which is then driven by the electric motor. Thus, by virtueof the electric compressor, the continuity of operation of theair-conditioning circuit and the maintaining of the comfort temperaturein the cabin are carried out when the engine has stopped.

It is necessary, however, to note that during the phases of stopping ofthe air-conditioning circuit, especially the engine stopping phasesimposed by the “Stop and Start” function, the cabin is in generalalready conditioned in comfort conditions, so that the refrigerativepower to be provided by the electric motor so as to maintain theseconditions for a duration limited to a few tens of seconds is lower, atleast by a factor of 2 to 3, than the power that must be provided by theengine. It is therefore possible to use for the electric compressor acompression chamber of reduced capacity driven by an electric motor oflow power.

However, when the air-conditioning circuit is taken out of operationfollowing an interruption of the driving of the mechanical compressor bythe engine, rearrangements of pressure of the refrigerant fluid canoccur along the air-conditioning circuit, which are liable to create aresistive torque which the electric motor must oppose at the moment atwhich it is harnessed to deputize for the stopping of the driving of themechanical compressor by the engine. Under these conditions, however,the power necessary to overcome this resistive torque can become greaterthan the sufficient power that the electric motor must develop in orderto maintain cabin comfort.

Hence, an aim of the invention is to propose a method for managing ahybrid compressor for an air-conditioning circuit of an engined motorvehicle, said hybrid compressor being able to be driven, on the onehand, by said engine, and, on the other hand, by an electric motorduring phases of interruption of driving of the compressor by theengine, which would make it possible to circumvent the difficultyrepresented by the use of an electric motor of too low power in regardto the resistive torque induced by the variations in refrigerant fluidpressure during the stoppage of the air-conditioning circuit.

This aim is achieved, in accordance with the invention, because saidmethod consists, during a driving interruption phase, in starting saidelectric motor before the commencement of said driving interruption.

Thus, the electric motor is set into operation by anticipation, beforethe engine stops driving the compressor and therefore before theair-conditioning circuit ceases to operate. The electric motor does nottherefore have to overcome the diverse variations in refrigerant fluidpressure which appear in the air-conditioning circuit following thecomplete stopping of the air-conditioning circuit. It is then possible,without any drawback, to use an electric motor of low power.

According to a first embodiment of the invention, in which said hybridcompressor comprising a first refrigerant fluid compression chambercomprising a first compression rod able to be driven by said engine anda second refrigerant fluid compression chamber comprising a secondcompression rod able to be driven by said electric motor, said methodcomprises steps consisting in detecting by anticipation a phase ofinterruption of driving of the first compression rod by the engine, inswitching the refrigerant fluid from the first to the second compressionchamber, and in starting the electric motor before the commencement ofthe interruption of driving of the first compression rod by the engine.

This first embodiment is implemented especially when said drivinginterruption is a stopping of the engine, and, more specially, when saidstopping of the engine is an automatic stopping determined by a functionfor automatic stopping and restarting of the engine of the vehicle, suchas the “Stop and Start” function.

According to a second embodiment of the invention in which said hybridcompressor comprising a variable-capacity refrigerant fluid compressionchamber comprising a single compression rod able to be driven by theengine in a higher interval of capacities and by the electric motor in alower interval of capacities, said method comprises steps consisting indetecting by anticipation a phase of interruption of driving of thecompression rod by the engine, in switching the capacity of thecompression chamber from the higher interval to the lower interval ofcapacities, and in starting the electric motor before the commencementof the interruption of driving of the compression rod by the engine.

The invention provides, generally, that said driving interruption is adecoupling of the engine from a compression rod of the hybridcompressor, and, more specially, that the decoupling of the engine isdetermined by a function for automatic stopping and restarting of theengine of the vehicle, such as the “Stop and Start” function, or by avehicle acceleration request.

In the case of a hybrid compressor with two separate compressionchambers, the decoupling is performed between the engine and the firstcompression rod, while in the case of a hybrid compressor with avariable-capacity compression chamber, the decoupling is performedbetween the engine and the single compression rod of the chamber.

In practice, the starting of the electric motor before the commencementof the interruption of driving of the hybrid compressor by the engine iscarried out by means for detecting stopping of the engine of a functionfor automatic stopping and restarting of the engine of the vehicle, orby means for detecting a vehicle acceleration request.

Within the framework of the “Stop and Start” function, these detectionmeans may be extremely varied and depend generally on the strategychosen by constructors. It is possible to cite for example the detectionof an action on the brake pedal when the speed of the vehicle goes belowa given threshold.

The description which follows with regard to the appended drawings,which are given by way of nonlimiting examples, will elucidate theinvention and the manner in which it may be embodied.

FIG. 1 is a diagram of an air-conditioning circuit comprising a hybridcompressor of a first type.

FIG. 2 is a diagram of an air-conditioning circuit comprising a hybridcompressor of a second type.

FIG. 3 is a chart illustrating the operation of the hybrid compressorsof FIGS. 1 and 2 for various life situations of a motor vehicle equippedwith the “Stop and Start” function.

FIG. 4 is a chart illustrating the operating chronology of the engineand electric motor of the hybrid compressors of FIGS. 1 and 2 duringautomatic stopping of the engine by the “Stop and Start” function,

In FIG. 1 is represented a conventional air-conditioning circuit of anengined motor vehicle, comprising a compressor 10 of a refrigerant fluidwhich may be an organic, inorganic or eutectic fluid. It is possible tocite as nonlimiting examples supercritical carbon dioxide CO2, therefrigerants known by the references R134A, 1234yf or else GAR (“GlobalAlternative Refrigerant”). Downstream of the compressor 10, thepressurized refrigerant fluid passes through a heat exchanger 11 calleda “gas cooler” for carbon dioxide or a “condenser” for R134A since, inthis case, the refrigerant initially in the gas phase exits thecondenser in liquid form.

In the example of FIG. 1, the exchanger 11 may be a water-typeexchanger, or an air-type exchanger cooled directly by the outside air.

The refrigerant fluid is thereafter conducted toward a relief valve 12so that it is cooled before entering the evaporator 13 where heatexchange then occurs between the cooled refrigerant and air blown towardthe cabin of the vehicle.

The refrigerant fluid, reheated on output from the evaporator 13, isthen returned to the compressor 10 to perform a new thermal cycle.

As may be seen in FIG. 1, the compressor 10 of FIG. 1 is a hybridcompressor of the type with two separate compression chambers, namely,on the one hand, a first chamber 101 comprising a first compression rod111 able to be driven by the shaft of the crankshaft of the engine (notrepresented) of the vehicle via a belt and a pulley 30 linkedmechanically to the rod 111 by way of a clutch 31, and, on the otherhand, a second chamber 102 comprising a second compression rod 112,independent of the first rod 111, able to be driven by an electric motor20.

During nominal operation of the air-conditioning circuit, the rod 111 ofthe first compression chamber 101 is driven by the engine, the pulley 30being coupled to the rod 111 by the clutch 31. The refrigerant fluidthen circulates through the first chamber 101 whose capacity, of theorder of 100 cm³, is chosen so as to allow the hybrid compressor 10 toensure an optimal comfort level inside the cabin of the vehicle,whatever the outside temperature, the sunshine and the degree ofrelative humidity.

However, it can happen, in certain circumstances, that theair-conditioning compressor 10 is no longer driven by the engine of thevehicle and that, consequently, the air-conditioning circuit ceases tooperate and can no longer guarantee the maintaining of the comforttemperature inside the cabin. Such is the case especially during theengine stopping phases determined by a system for automatic stopping andrestarting of the engine able to implement the “Stop and Start” functionof the vehicles equipped with this function.

In order to ensure continuity of air-conditioning in the cabin, thecirculation of refrigerant fluid is switched from the first chamber 101to the second chamber 102 by a valves device internal to the hybridcompressor 10, and then the electric motor 20 is started so as to drivethe second compression rod 112 and maintain the air-conditioning circuitin operation during these stopping phases.

When the electric motor 20 takes over from the then stopped engine, thecabin of the vehicle is in principle already at the comfort temperature,so that, having regard to the fact that the duration of the stoppingphases is generally limited to a few tens of seconds, the refrigerativepower to be provided by the electric motor 20 is relatively low. By wayof example, in a conventional manner, a refrigerative power of 6 kW isnecessary in order to guarantee comfort in the cabin of a vehicleexposed to a high temperature of 25 to 45° C. under sunshine of 1000W.m² and relative humidity of 50 and 60%. However, when the vehicle isalready conditioned to the comfort temperature, the refrigerative powerto be provided lies between 1 kW and 3 kW depending on the segment ofthe vehicle.

Consequently, the capacity of the second compression chamber 102 can belimited, with respect to the capacity of the first chamber 101, tovalues of about 20 cm³ for example.

In the chart of FIG. 3 have been represented the operating states of theengine and of the electric motor 20 for driving the hybrid compressor 10of a motor vehicle equipped with the “Stop and Start” function, thevalue 0 corresponding to the stopping of the motor and the value 1 toits operation.

As may be seen in this figure, when the first compression rod 111 is nolonger driven by the engine because the latter is stopped automaticallyin accordance with the “Stop and Start” function, the electric motor 20is set into operation so as to drive the rod 112 of the secondcompression chamber 102 and thus ensure maintenance of the comfort inthe cabin during the engine stopping phase.

However, it is necessary to emphasize that, under these conditions, theelectric motor 20 must provide, on starting, sufficient torque toovercome the resistive torque induced by the rearrangements ofrefrigerant fluid pressure which occur in the air-conditioning circuitat the moment of the stopping of the engine. The torque to be providedby the electric motor 20 then becomes very significant and demandshigher powers than those which are strictly necessary to ensure themaintaining of the air-conditioning.

Hence, to avoid a superfluous over-rating of the electric motor 20, theinvention proposes a method for managing the hybrid compressor 10comprising the steps consisting in detecting by anticipation a phase ofinterruption of driving of the first compression rod 111 by the engine,in switching the refrigerant fluid from the first 101 to the second 102compression chamber, and in starting the electric motor 20 before thecommencement of the interruption of driving of the first compression rod111 by the engine. In this way, the electric motor 20 is set intooperation before the stopping of the air-conditioning circuit andtherefore before the occurrence of any pressure rearrangements in theair-conditioning circuit. The power of the electric motor 20 cantherefore be rated accordingly.

To carry out the anticipation of the starting of the electric motor 20,it is possible to use the means implemented by the “Stop and Start”function to detect whether the engine stopping conditions are satisfiedand impose a stopping of the engine if these conditions are satisfied.

This is what is represented by FIG. 4 in which it is seen that as soonas conditions of automatic stopping of the engine are detected by the“Stop and Start” function, a signal of anticipation of starting of theelectric motor 20, generated for example by the onboard computer, isdispatched before the actual stopping of the engine toward the controlcircuit of the electric motor through the vehicle's CAN (“Car AreaNetwork”) network. The conditions of automatic stopping of the enginedepend on the strategy adopted by the vehicle constructor. It ispossible to cite, inter alia, an action on the brake pedal when thevehicle is traveling at low speed, less than 5 km/hour for example.

FIG. 4 shows another circumstance in which the electric motor 20 may beset into operation so as to guarantee the continuity of the comforttemperature during a stoppage of the air-conditioning circuit. Thissituation is that of an acceleration of the vehicle when requiring thebest response to the acceleration request by applying a maximum torqueto the shaft of the crankshaft, obtained by recovering the resistivetorque due to the driving of the compressor. In this circumstance, theinterruption of the driving of the first compression chamber 101 is notrelated to a stopping of the engine, but to the decoupling of the pulley30 for driving the compression rod 111 of the chamber.

In this case, the electric motor 20 is started as soon as theacceleration request is detected by usual detection means and before theengine is actually decoupled from the compression rod 111.

In FIG. 2 is represented a hybrid compressor 10′ of the type comprisinga variable-capacity compression chamber 100 whose rod 110 may be driven,either by the electric motor 20, or by the shaft of the crankshaft ofthe engine (not represented) of the vehicle via a belt and the pulley 30able to be linked mechanically to the rod 110 by way of the clutch 31.

It is necessary to emphasize here that this architecture of hybridair-conditioning compressor is distinguished from the compressor of FIG.1 by the fact that it implements only a single compression chamber and asingle rod that can equally well be driven by the engine or by theelectric motor, instead of two separate compression chambers ofindependent rods.

During nominal operation, the rod 110 of the compression chamber 100 isdriven by the engine, the pulley 30 being coupled to the rod 110 by theclutch 31. The capacity of the compression chamber is then chosen in ahigher interval of values close to the maximum capacity, of the order of100 cm³ for example. Under these conditions, the hybrid compressor 10′is capable of ensuring an optimal comfort level inside the cabin of thevehicle, whatever the outside temperature, the sunshine and the degreeof relative humidity.

However, it can happen, just as for the hybrid compressor 10 with twochambers of FIG. 1, that the air-conditioning compressor 10′ is nolonger driven by the engine of the vehicle and that, consequently, theair-conditioning circuit ceases to operate and no longer ensuresmaintenance of the comfort temperature inside the cabin. Such is thecase, as seen above, during the engine stopping phases determined by afunction for automatic stopping and restarting of the “Stop and Start”type, or during the vehicle acceleration request phases.

In order to ensure continuity of air-conditioning in thesecircumstances, the electric motor 20 is set into operation during thephases of stopping of driving of the compressor 10′ by the engine.Stated otherwise, it may be considered that the electric motor 20 thensubstitutes itself for the engine in its function of driving thecompression chamber 100. Of course, the engine is, preferably,disengaged from the compression rod 110.

It was already mentioned above that the refrigerative power to beprovided by the electric motor 20 during operation is relatively low.

Consequently, the capacity of the compression chamber 100 may bereduced, with respect to the nominal operating conditions, to valueslying in a lower interval of capacities of about the minimum capacity of20 cm³ for example.

Of course, the higher and lower intervals of capacities may be reducedsimply to the maximum and minimum capacities alone. The compressionchamber 110 then switches in a binary manner between these twocapacities depending on whether the motive drive for the rod of thechamber is the engine or the electric motor.

Having regard to the fact that the power requested of the electric motor20 is relatively low, it is possible to envisage the use of an electricmotor, with or without brushes, supplied by a low-voltage direct currentprovided, in particular, by the 12 V network of the vehicle, it beingpossible for the electric current source to be a battery 40 or an extraunit furnished or not with a storage capacitor.

In a practical manner, the variable-capacity compression chamber 100 maybe embodied by a conventional compression chamber with vanes whoseintake volume, corresponding to the capacity, can be adjusted betweenthe minimum value of 20 cm³, for example, and the maximum value of 100cm³, for example, by varying the position of the intake orifice in thechamber.

Just as for the hybrid compressor 10 of FIG. 1, it is possible to avoidthe electric motor 20 having to provide a torque increased by theresistive torque resulting from the rearrangements of refrigerant fluidpressure upon the stopping of the air-conditioning circuit by theimplementation of a method for managing the hybrid compressor 10′comprising steps consisting in detecting by anticipation a phase ofinterruption of driving of the compression rod 110 by the engine, inswitching the capacity of the compression chamber 100 from the higherinterval to the lower interval of capacities, and in starting theelectric motor 20 before the commencement of the interruption of drivingof the compression rod 110 by the engine.

Whether the interruption of driving of the compressor 10′ by the engineis due to an automatic stopping determined by the “Stop and Start”function or to an acceleration request, the transition between thedriving of the compression rod 110 by the engine and driving by theelectric motor 20 is performed by decoupling the pulley 30 from thecompression rod 110 by means of the clutch 31.

The sought-after anticipation for setting the electric motor 20 intooperation is obtained, in accordance with FIG. 4, by starting theelectric motor before the actual decoupling of the engine from thecompression rod 110.

The means for detecting a stopping of the engine or an accelerationrequest are the same as those used for the compressor 10 of FIG. 1, asis the control of the electric motor 20 by a starting anticipationsignal.

1. A method for managing a hybrid compressor for an air-conditioningcircuit of an engine motor vehicle, the hybrid compressor being able tobe driven by said engine and by an electric motor during phases ofinterruption of driving of the compressor by the engine, the methodcomprising: during a driving interruption phase, starting said electricmotor before commencement of said driving interruption.
 2. The method asclaimed in claim 1, wherein the hybrid compressor comprises: a firstrefrigerant fluid compression chamber comprising a first compression rodable to be driven by said engine, and a second refrigerant fluidcompression chamber comprising a second compression rod able to bedriven by said electric motor, wherein the method further comprises:detecting by anticipation a phase of interruption of driving of thefirst compression rod by the engine, switching the refrigerant fluidfrom the first to the second compression chamber, and starting theelectric motor before commencement of the interruption of driving of thefirst compression rod by the engine.
 3. The method as claimed in claim1, wherein the hybrid compressor comprises: a variable-capacityrefrigerant fluid compression chamber comprising a single compressionrod able to be driven by the engine in a higher interval of capacitiesand by the electric motor in a lower interval of capacities, wherein themethod further comprises: detecting by anticipation a phase ofinterruption of driving of the compression rod by the engine, switchingthe capacity of the compressing chamber from the higher interval to thelower interval of capacities, and starting the electric motor beforecommencement of the interruption of driving of the compression rod bythe engine.
 4. The method as claimed in claim 2, wherein said drivinginterruption is a stopping of the engine.
 5. The method as claimed inclaim 4, wherein said stopping of the engine is an automatic stoppingdetermined by a function for automatic stopping and restarting of theengine of the vehicle (“Stop and Start”).
 6. The method as claimed inclaim 2, wherein said driving interruption is a decoupling of the enginefrom a compression rod of the hybrid compressor.
 7. The method asclaimed in claim 6, wherein the decoupling of the engine is determinedby a function for automatic stopping and restarting of the engine of thevehicle (“Stop and Start”).
 8. The method as claimed in claim 6, whereinthe decoupling of the engine is determined by a vehicle accelerationrequest.
 9. The method as claimed in claim 1, wherein the starting ofthe electric motor before the commencement of the interruption ofdriving of the hybrid compressor by the engine is carried out by meansfor detecting stopping of the engine of a function for automaticstopping and restarting of the engine of the vehicle (“Stop and Start”).10. The method as claimed in claim 8, wherein the starting of theelectric motor before the commencement of the interruption of driving ofthe hybrid compressor by the engine is carried out by means fordetecting a vehicle acceleration request.